The Brevo WordPress plugin suffers from an authorization bypass vulnerability caused by PHP type juggling in the `/wp-json/mailin/v1/mailin_disconnect` REST API endpoint. The plugin uses loose comparison (==) to validate the installation ID, which allows an attacker to send a boolean true value for the `id` parameter and bypass authorization. Exploiting this flaw, an unauthenticated attacker can disconnect the Brevo integration, delete the API key, remove all subscription forms, and reset plugin settings. The vulnerability affects all versions up to and including 3.3.0. The CVSS v3.1 base score is 6.5, reflecting network attack vector, low attack complexity, no privileges required, no user interaction, unchanged scope, no confidentiality impact, limited integrity impact, and high availability impact.

An unauthenticated attacker can bypass authorization controls to disconnect the Brevo integration, delete the API key, remove all subscription forms, and reset plugin settings. This results in loss of plugin functionality and potential denial of service for email, SMS, web push, and chat features provided by the plugin. There is no direct confidentiality impact reported.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, restrict access to the vulnerable REST API endpoint if possible and monitor for suspicious requests targeting `/wp-json/mailin/v1/mailin_disconnect`. Avoid exposing this endpoint publicly or implement additional access controls as a temporary mitigation.